Split fin for a heat exchanger

ABSTRACT

The efficiency of a heat exchanger used in applications where heat conduction between rows of conduits located from front to back of the heat exchanger and provided with common fins ( 42 ) is increased where the fins ( 42 ) are abutted to adjacent tube runs ( 22,24,26 ) in each row and extend from the front ( 28 ) to the back ( 30 ) of the heat exchanger so each fin ( 42 ) is common to each of the rows ( 22,24,26 ). Heat flow interrupters ( 56,58 ) are located in each fin ( 42 ) at locations aligned with spaces ( 27 ) between the runs ( 22,24,26 ). Each heat flow interrupter ( 56,58 ) is defined by a slit ( 62 ) extending completely through the fin  42  which is characterized by the absence of the removal of any material of which the fin ( 42 ) is made at the slit ( 62 ).

FIELD OF THE INVENTION

[0001] This invention relates to a split fin construction for use inheat exchangers, and more particularly, for a heat exchanger having aplurality of rows of tube runs from front to back and wherein it isdesirable to minimize heat transfer through the fin from one row oftubes to another.

BACKGROUND OF THE INVENTION

[0002] There are a variety of applications wherein it is important tolimit heat conduction between the front and rear side of a heatexchanger. Such applications are typified by those wherein the fluidtemperature entering the heat exchanger is at a significantly differentlevel than the temperature of the fluid exiting the heat exchanger. Onesuch application is in a refrigeration system heat exchanger such as acondenser, or more specifically, a gas cooler and a refrigeration systemutilizing a transcritical refrigerant. CO₂ is an example of such arefrigerant.

[0003] Another application occurs where two or more heat exchangercores, each receiving a separate fluid, are located in series in theflow path for another heat exchange fluid such as a gas as air. Anexample of such an application would be one usually found in a vehicularcontext wherein, for example, the core of a condenser or gas cooler foran air conditioning system is located upstream or downstream of a corefor engine coolant.

[0004] In the former case, in order to decrease the refrigerant exittemperature as much as possible, it is desired to limit the conductionpath across the depth of the heat exchanger such that the relativelymuch hotter entering refrigerant dissipates its heat to the coolantpassing through the heat exchanger rather than to the exitingrefrigerant via conduction through fins extending from front to back inthe heat exchanger. In the latter case, it is desirable that heat fromthe radiator and the engine coolant therein is not conveyed to thecondenser via common fins to impede the efficiency of operation of thecondenser or vice versa.

[0005] In a typical gas cooled heat exchanger, cross conduction pathsmay exist both in the metal tubes as well as the metal fins. To avoidthe formation of a cross conduction path in the metal tubes, the tubesin adjacent rows from front to back of the heat exchanger are spacedfrom one another. To minimize cross conduction through the fins, heatinterrupters, typically in the form of slots, are located in the fins inalignment with the spaces between the rows of tubes in the heatexchanger. Examples of the latter are shown, for example, in ShinmuraU.S. Pat. No. 5,000,257 and its reissue U.S. Pat. NO. Re. 35,710;Sugimoto U.S. Pat. No. 5,992,514; Watanabe U.S. Pat. No. 5,720,341 andYamanaka U.S. Pat. No. 6,000,460.

[0006] In each of the foregoing patents, a slot is formed whereinmaterial is removed from the fin to form the slot which provides aninterruption in the heat conduction through the fin. While theseconstructions are believed to be operative for their intended purpose,the fact that material is removed from the fin reduces the surface areaof the fin. As is apparent from Fourier's law, a reduction in areareduces heat transfer and thus the slots proposed by the abovepatentees, while providing the desired reduction in heat conductionthrough the fin from one side of the heat exchanger to the other, alsoincrease gas side thermal resistance, reducing the efficiency of heatexchange from the fluid contained within the tubes to a gas which passesthrough the fins. As, in typical gas/fluid heat exchangers, gas sidethermal resistance can account for as much as 95% of the totalresistance to heat exchange from the gas to the fluid flowing within thetubes, it is highly desirable that reduction of heat conduction throughthe fin from one side of the heat exchanger to the other not beaccompanied by an increase in gas side thermal resistance.

[0007] The present invention is directed to achieving that desire.

SUMMARY OF THE INVENTION

[0008] It is a principal object of the invention to provide a new andimproved gas side fin for use in heat exchangers having plural rows oftube runs from front to back of the heat exchanger. More specifically,it is an object of the invention to provide such a fin wherein heatconduction through the fin from one side of the heat exchanger to theother is minimized while at the same time is not accompanied by anincrease in gas side thermal resistance.

[0009] An exemplary embodiment of the invention accomplishes theforegoing in a heat exchanger having a front and a back with a pluralityof spaced rows of flattened tubes from front to back which definealigned tube runs in each row. Serpentine fins are abutted to adjacenttube runs in each row and extend from front to back so that each fin iscommon to each of the rows. The serpentine fins have heat flowinterrupters in each fin at a location in the space between the alignedtube runs in each row. The invention contemplates the improvementwherein the heat flow interrupter is defined by a slit extendingcompletely through the fin and which is characterized by the absence ofthe removal of any material of which the fin is made at the slit.

[0010] In a preferred embodiment, the edges of the slit are displacedfrom the remainder of the fin.

[0011] In one embodiment, the edges of the slit extend at an acute angleto the remainder of the fin.

[0012] Even more preferably, the edges of each slit are displaced inopposite directions from the remainder of the fin at the acute angle.

[0013] In another embodiment of the invention, the edges of each slitare displaced into offset, spaced planes.

[0014] In still another embodiment of the invention, the slits in eachfin defining the heat flow interrupters in each fin are separated byshort joining sections and the edges of each slit are spaced from oneanother by deforming the joining sections.

[0015] Preferably, the joining sections are made thinner than theremainder of the fins. By way of example only, a coining operation maybe utilized on the joining sections to make them thinner therebydisplacing the edges of the slit into spaced relation.

[0016] In a preferred embodiment, the aligned ones of the tube runs areconnected in hydraulic series so as to be useable as a gas cooler or agas cooler/evaporator in a refrigeration system or in a heat pumpsystem.

[0017] Other objects and advantages will become apparent from thefollowing specification taken in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a somewhat schematic perspective view of a heatexchanger made according to the invention;

[0019]FIG. 2 is an enlarged, fragmentary sectional view takenapproximately along the line 2-2 in FIG. 1;

[0020]FIG. 3 is a fragmentary sectional view taken approximately alongthe line 3-3 in FIG. 2;

[0021]FIG. 4 is a fragmentary sectional view taken approximately alongthe line 4-4 in FIG. 2 and showing a modified embodiment of theinvention;

[0022]FIG. 5 is a fragmentary sectional view taken approximately alongthe line 5-5 in FIG. 2 and showing still another modified embodiment ofthe invention;

[0023]FIG. 6 is a view similar to that taken along the line 5-5 in FIG.2 but showing still a further modified embodiment; and

[0024]FIG. 7 is a schematic of a refrigeration system, specifically aheat pump system, in which a heat exchanger having a fin made accordingto the invention may be employed.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0025] The following description will describe the invention generallyin the terms of a refrigeration system which is intended to encompassheat pump systems as well. The context of the description will be thatof a vehicular heating/cooling system but it is to be specificallyunderstood that the invention is not limited to use in vehicularsystems. The invention will also be described in the context of a gascooler wherein a gas, typically air, is utilized to cool and/or condensea single fluid such as a refrigerant; and the term “gas cooler” isintended to include both condensers and coolers which cool refrigerantwithout condensing it. However, the invention is also applicable to heatexchangers having a plurality of cores, each receiving a differentworking fluid as, for example, a plural core heat exchanger for coolingboth the refrigerant from a gas cooler and the coolant for an engine orthe like. Similarly, while the invention will be described in thecontext of a gas, typically air, cooling another working fluid withinthe heat exchanger, it should be appreciated that the heat exchanger canbe employed wherein the gas is heated by the working fluid as well. Inshort, the invention is not to be limited by the following descriptionexcept in so far as stated in the appended claims.

[0026] Referring to FIG. 1, a heat exchanger made according to theinvention is illustrated and is seen to include a pair of spaced,parallel, tubular headers 10,12. Of course, header plates fitted withtanks could be employed in lieu of the tubular headers 10,12 if desired.

[0027] In the illustrated embodiment, the header 10 is provided with anoutlet schematically illustrated at 14 while the header 12 is providedwith an inlet, schematically indicated at 16. A direction of air flowthrough the heat exchanger is illustrated by an arrow 18 and it will beseen that the just described arrangement of the inlet 16 and outlet 14provide a counter/cross flow heat exchange regime. However, in someinstances the air flow direction 18 can be reversed.

[0028] When the heat exchanger is intended to be used as a gas cooler orgas cooler/evaporator in a refrigeration system, the foregoingcounter/cross flow arrangement is preferred. That is also true of theuse of tubular headers 10,12 because of their high pressure resistance.

[0029] A plurality of flattened tubes 20 extend between the headers10,12 that are in fluid communication with the interior of each. Eachflattened tube is configured in a serpentine configuration so as to havethree runs 22, 24 and 26 which are parallel with each other and whichare aligned with each other from the front 28 of the heat exchanger tothe rear 30 thereof. Consequently, the runs 22 form a front row of runswithin the heat exchanger, the runs 24 form an intermediate row of runswithin the heat exchanger and the runs 26 form a rear row of runs withinthe heat exchanger. The runs 22, 24 and 26 are spaced by a small gap 27(FIG. 2) so as to prevent or otherwise minimize heat conduction betweenthe runs 22, 24 and 26 as would result if they were in contact with oneanother.

[0030] The various runs are connected by arcuate sections 32. In theusual case, the arcuate sections 32 will be approximately in line withone or the other of the headers 10,12 in the direction of air flow 18through the heat exchanger. Preferably, the tubes making up the runs22,24,26 and the arcuate sections 32 are flattened tubes having a majordimension DM and a minor dimension Dm transverse thereto. Desirably, tomaximize the cross sectional area of the gas flow path through the heatexchanger, the runs 22,24,26 are oriented so that the major dimension DMis parallel to the direction of air flow 18 through the heat exchanger.

[0031] At the same time, in high pressure applications, such as gascoolers used in transcritical refrigeration systems, it is desirablethat the diameter of the headers 10,12, be as small as possible. Thus,it is conceivable, and even likely that the tube major dimension DM willbe greater than the diameter of either of the headers 10 or 12. In sucha case, the ends of the runs 22,26, shown collectively at 34, arereceived in elongated slots 36 in the respective headers 10,12 whichextend in the direction of elongation of the respective header 10,12. Toachieve this relation along with the relation requiring the tube majordimensions DM to be parallel to the direction of air flow 18,immediately adjacent to the ends 34, the tubes are provided with a twist38, typically, but not always, 90°. Similar twists are also provided atthe ends of each arcuate section 32 and are schematically illustrated bydotted lines 40. The twists 40 facilitate bending of the tubes toinclude the arcuate sections 32.

[0032] Serpentine fins, generally designated 42, are disposed betweenadjacent ones of the tubes with each fin 42 extending between an alignedpair of the runs 22, the runs 24 and the runs 26 from the front 28 tothe back 30 of the heat exchanger. Alternatively plate or other fins maybe used. Thus, there exists a heat conductive flow path between the runs22, 24 and 26 through the fins 42.

[0033] As generally alluded to previously, it is undesirable in manyapplications that such a heat conduction path exists. As mentionedpreviously, those applications include ones where a sizable temperaturedifferential exists between the runs 22 and 26 as would be the case in agas cooler or gas cooler/evaporator when being operated as a gas coolerin a transcritical refrigeration system. Another typical example wouldbe where certain of the runs are being employed in a condenser for arefrigerant and others of the runs are being employed as a radiator forcoolant such as engine coolant. In the case of the latter, of course,additional headers to separate the refrigerant stream from the coolantstream would be employed.

[0034] As seen in FIG. 1, each of the fins 42 includes a plurality ofgenerally flat sections 44, which are connected to each other by crests46, which, in turn, are metallurgically bonded as by brazing, solderingor welding, to the flat side of each of the tube runs 22,24,26 betweenwhich the fin 42 is located.

[0035] As seen in FIG. 2, each section 44 is defined by three segmentsincluding a first segment 48 extending between the tube runs 22, asecond segment 50 extending between the tube runs 24 and a third segment52 extending between the tube runs 26. Each of the segments 48,50,52 istypically provided with louvers 54 which may be of conventionalconstruction.

[0036] Between each of the segments 48,50,52 is a flow interrupter. Twosuch flow interrupters are shown in FIG. 2 which are made according todifferent embodiments of the invention. A first flow interrupter isgenerally designated 56 while a second is generally designated 58.According to the invention, each flow interrupter is defined by anelongated slit that runs continuously through each fin 44 and ispositioned to be located in alignment with the spaces 27 between theruns 22, 24 and 26. The slits are illustrated at 62 in FIG. 2 and eachis interrupted by connecting sections 64 that may be a few millimetersin length and which are positioned at intervals in the correspondingslit 62. The connecting sections 64 need not be present at each section44 of each fin 42 and typically will not be. They only need be providedwith such frequency as to maintain the integrity of a fin 42 so that itwill not separate into individual parts at each slit 62.

[0037] The slits 62 are generally straight line and have opposed edges.As illustrated in FIG. 3, the opposed edges are shown at 66 and 68, faceone another and are generally transverse to the direction of air flow18. In the embodiment of the invention illustrated in FIG. 3, the edges66 and 68 are virtually in abutment, but not quite in abutment, witheach other, and, because of the interruption in the continuity of thefin 42 at this location, interrupt the flow of heat from one segment48,50,52 to the other. It is to be particularly noted that the slits 62are formed without the removal of any material from the fin 42 itself.As a consequence, the surface area of each fin 42 is not diminished inany way by the presence of the slits 62 and as a consequence, each fin42 has a maximum surface area for heat exchange of air flowing in thedirection 18. Consequently, the greater surface area of each fin thatresults provides improved heat transfer.

[0038] In the embodiment shown in FIG. 3, it is desirable, though notabsolutely necessary, that if braze material is employed, that brazematerial be located on the side walls 70 of the tube runs 22,24,26 asopposed to being on the fin 42. This assures that the slit 62 willremain continuous after it is formed as a result of the prevention offlow of brazed metal into the slit 62 that might braze the edges 66,68together.

[0039] The embodiment of FIG. 4 provides further assurance that therewill be no brazing together of the edges 66,68 of each slit 62. In thisembodiment, the segments 50 of each fin 42 which extend between the tuberuns 24 are displaced in the direction of elongation of the tube runs22,24,26 from segments 48,52 without the removal of any material fromthe fin 42. As a result, gaps 70 in a plane generally transverse to theplane of each segment 48,50,52 are provided to define the flowinterrupters 56.

[0040] Still another alternative is illustrated in FIG. 5. In theembodiment of FIG. 5, one of the flow interrupters 58 is illustrated.One edge 72 of the slit 62 is bent upwardly while another edge 74 isbent downwardly so that the two edges 72,74 are spaced as illustrated inFIG. 5. Again, a gap between the edges 72,74, is formed as in theembodiment of FIG. 4 as well, and again, without the removal of anymaterial from the fin 42 which would reduce its surface area.

[0041]FIG. 6 illustrates still another embodiment of the invention. Inthis embodiment, the joining sections 64 are compressed by a suitableoperation as, for example, by coining. This results in the edges of theslits 72,74 being driven away from one another even though occupying thesame plane so as to form a gap 76 between adjacent ones of the segments48,50,52. Since the coining operation does not cause removal of anymaterial from the fin, fin surface area is again maximized to improveheat transfer.

[0042]FIG. 7 illustrates a preferred environment of use of heatexchanger made according to the invention. Specifically illustrated is arefrigeration system as may be used for refrigeration or airconditioning purposes, and more specifically, a heat pump system whichmay be employed for both heating and cooling. Two heat exchangers,generally designated 80 and 82, respectively, and made according to theinvention are employed as gas cooler/evaporators with one acting as agas cooler when the other is acting as an evaporator, and vice versa.The two are connected in a conventional heat pump circuit with valves 84as is a conventional compressor 86 and an expansion valve 88. Typicallya suction line heat exchanger (not shown) will be located on the inletside 90 of the compressor 86 along with an accumulator (also not shown).

[0043] When the system in FIG. 7 is employed for cooling purposes, theheat exchanger 80 will be acting as a gas cooler and will receivecompressed refrigerant from the outlet side 92 of the compressor 86 viathe heat pump connected plumbing and valves 84 on a line 94. Thecompressed, hot refrigerant will exit the heat exchanger 80, now actingas a gas cooler on a line 96 to ultimately be passed through theexpansion valve 88 which discharges on a line 98 connected to the heatexchanger 82. The refrigerant will be expanded in the heat exchanger 82,now acting as an evaporator, and ultimately returned to the inlet side90 of the compressor 86 via the previously mentioned suction line heatexchanger, if present. Conventional fans 100 are employed to drive airthrough both of the heat exchangers 80,82.

[0044] When the system of FIG. 7 is employed for heating purposes, theheat exchanger 82 will be employed as a gas cooler and the heatexchanger 80 as an evaporator. In this case, hot compressed refrigerantfrom the outlet side 92 of the compressor 86 will be provided to theheat exchanger 82 on the line 98 to exit therefrom on a line 102 whichwill be connected by the heat pump connected plumbing and valves 84 tothe expansion valve 88. From the expansion valve 88, the refrigerantwill enter the heat exchanger 80 on the line 94 and expand therein asthe heat exchanger 80 will be acting as an evaporator at this time. Therefrigerant exiting the heat exchanger 80 will exit on the line 96 to bereturned via the heat pump connected plumbing and valves 84 to the inletside 90 of the compressor 86.

[0045] From the foregoing, it will be appreciated that a heat exchangermade according to the invention is ideally suited for those applicationswhere heat conduction through fins common to several rows of runs oftubing is highly undesirable. The provision of the slits 62 in the fins54 between the segments 48, 50 and 52 to act as heat interruptersachieves that function without the removal of any of the material ofwhich the fins 42 are made. Consequently, the fins 42 retain theiroriginal surface area which then is available for heat transfer, makingthe fins 42 more efficient that those fins heretofore known whichinvolve the removal of material from the fins to provide the heatinterrupters.

[0046] The invention is not only applicable to those heat exchangerswherein a large temperature differential from one run to the next isencountered where all of the runs contain a single working fluid such asa refrigerant, but may be used with efficacy in combination heatexchangers such as common core condensers and radiators wherein the finsare common to both the condensing section and the radiator section.

[0047] The heat interrupters 56,58 are easily fabricated during thetypical roll forming operation used to provide the serpentine fins 42which provides a simple and economical way to accomplish the desiredresult without the necessity of removing material from the fins 52 anddisposing of the scrap constituted by such removed material.

[0048] Finally, it will be appreciated that in some instances, theprinciples of the invention are not limited to serpentine fin heatexchangers but may be employed in plate fin heat exchangers as well.

1. In a heat exchanger having a front and a back, a plurality of spacedrows of flattened tubes from front to back and defining aligned tuberuns in each row, and fins abutted to adjacent tube runs in each row andextending from front to back so that each fin is common to each of saidrows and having heat flow interrupters in each fin at a location in thespace between the aligned tube runs in each row, the improvement whereineach said heat flow interrupter is defined by a slit extendingcompletely through the fin and is characterized by the absence of theremoval of any material of which the fin is made at the slit.
 2. Theheat exchanger of claim 1 wherein the edges of the slit are displacedfrom the remainder of the fin.
 3. The heat exchanger of claim 2 whereinthe edges of the slit extend at an acute angle to said remainder of thefin.
 4. The heat exchanger of claim 3 wherein the edges of each slit aredisplaced in opposite directions from said remainder of the fin to saidacute angle.
 5. The heat exchanger of claim 2 wherein the edges of eachslit are displaced into offset, spaced planes.
 6. The heat exchanger ofclaim 1 wherein the slits in each fin defining said heat flowinterrupter in each fin are separated by short joining sections and theedges of each slit are spaced from one another by deforming said joiningsections.
 7. The heat exchanger of claim 6 wherein said joining sectionsare thinner than the remainder of said fins.
 8. In a heat exchangerhaving a front and a back, a plurality of spaced rows of flattened tubesfrom front to back and defining aligned tube runs in each row, andserpentine fins abutted to adjacent tube runs in each row and extendingfrom front to back so that each fin is common to each of said rows andhaving heat flow interrupters in each fin at a location in the spacebetween the aligned tube runs in each row, the improvement wherein eachsaid heat flow interrupter is defined by a slit extending completelythrough the fin and is characterized by the absence of the removal ofany material of which the fin is made at the slit, the aligned ones ofsaid tube runs being connected in hydraulic series.
 9. In a heatexchanger having a front and a back, a plurality of spaced rows offlattened tubes from front to back and defining aligned tube runs ineach row, and serpentine fins abutted to adjacent tube runs in each rowand extending from front to back so that each fin is common to each ofsaid rows and having heat flow interrupters in each fin at a location inthe space between the aligned tube runs in each row, the improvementwherein each said heat flow interrupter is defined by a slit extendingcompletely through the fin and is characterized by the absence of theremoval of any material of which the fin is made at the slit, said slithaving parallel edges displaced in opposite directions from a remainderof the fin.
 10. The heat exchanger of claim 9 wherein the edges of theslit are displaced from the remainder of the fin.
 11. In a heatexchanger having a front and a back, a plurality of spaced rows offlattened tubes from front to back and defining aligned tube runs ineach row, and serpentine fins abutted to adjacent tube runs in each rowand extending from front to back so that each fin is common to each ofsaid rows and having heat flow interrupters in each fin at a location inthe space between the aligned tube runs in each row, the improvementwherein each said heat flow interrupter is defined by a slit extendingcompletely through the fin and is characterized by the absence of theremoval of any material of which the fin is made at the slit, said slithaving edges displaced into offset, spaced planes.
 12. In a heatexchanger having a front and a back, a plurality of spaced rows offlattened tubes from front to back and defining aligned tube runs ineach row, and serpentine fins abutted to adjacent tube runs in each rowand extending from front to back so that each fin is common to each ofsaid rows and having heat flow interrupters in each fin at a location inthe space between the aligned tube runs in each row, the improvementwherein each said heat flow interrupter is defined by a slit extendingcompletely through the fin and is characterized by the absence of theremoval of any material of which the fin is made at the slit, said slitshaving edges with the slits in each fin defining said heat flowinterrupter in each fin are separated by short joining sections and theedges of each slit are spaced from one another by deforming said joiningsections.
 13. In a refrigeration system containing a transcriticalrefrigerant, a compressor for compressing the refrigerant, an evaporatorconnected to an inlet of the compressor and for evaporating therefrigerant, and a gas cooler for receiving compressed refrigerant fromthe compressor, cooling the same and discharging the cooled refrigerantto the evaporator, the improvement wherein the gas cooler comprises aheat exchanger having a front and a back, a plurality of spaced rows offlattened tubes from front to back and defining aligned tube runs ineach row, and serpentine fins abutted to adjacent tube runs in each rowand extending from front to back so that each fin is common to each ofsaid rows and having heat flow interrupters in each fin at a location inthe space between the aligned tube runs in each row, the improvementwherein each said heat flow interrupter is defined by a slit extendingcompletely through the fin and is characterized by the absence of theremoval of any material of which the fin is made at the slit.
 14. Theheat exchanger of claim 13 wherein the edges of the slit are displacedfrom the remainder of the fin.
 15. The heat exchanger of claim 14wherein the edges of the slit extend at an acute angle to said remainderof the fin.
 16. The heat exchanger of claim 15 wherein the edges of eachslit are displaced in opposite directions from said remainder of the finto said acute angle.
 17. The heat exchanger of claim 14 wherein theedges of each slit are displaced into offset, spaced planes.
 18. Theheat exchanger of claim 13 wherein the slits in each fin defining saidheat flow interrupter in each fin are separated by short joiningsections and the edges of each slit are spaced from one another bydeforming said joining sections.
 19. The heat exchanger of claim 18wherein said joining sections are thinner than the remainder of saidfins.
 20. The refrigeration system of claim 13 wherein said system is aheat pump system wherein said evaporator is also a gas cooler and saidgas cooler is also an evaporator.